Composite article having a ceramic nanocomposite layer

ABSTRACT

A composite article includes a substrate and a ceramic nanocomposite layer disposed on the substrate. The ceramic nanocomposite layer has a composition that includes silicon, boron, carbon and nitrogen.

BACKGROUND

This disclosure relates to composite articles having a ceramicprotective layer for improved thermal and oxidative protection.

Ceramic and metallic materials, such as superalloys, are attractivematerials for use in articles that operate under severe environmentalconditions. As an example, gas turbine engine components are subjectedto high temperatures, corrosive and oxidative conditions, and elevatedstress levels. In order to improve the thermal and oxidative stabilityof these components, various types of barrier layers have been used toprotect the underlying substrate from the elevated temperatureconditions or corrosive/oxidative environment.

SUMMARY

An exemplary composite article includes a substrate and a ceramicnanocomposite layer disposed on the substrate. The ceramic nanocompositelayer has a composition that includes silicon, boron, carbon andnitrogen.

In another aspect, a composite article includes a silicon-based ceramicsubstrate and a ceramic nanocomposite layer disposed on the substrate.The ceramic nanocomposite layer has a composition that includes silicon,boron, carbon and nitrogen and at least one oxide-forming element fromaluminum, titanium, zirconium, hafnium, vanadium, niobium, tantalum,chromium, molybdenum, tungsten, yttrium, ytterbium, scandium, rhenium,and combinations thereof.

An exemplary method of processing a composite article includes formingthe ceramic nanocomposite layer having the composition that includessilicon, boron, carbon and nitrogen on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the disclosed examples willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example composite article having a ceramicnanocomposite layer.

FIG. 2 illustrates another example composite article having a ceramicnanocomposite layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates selected portions of an example composite article 20having improved thermal and oxidative stability, for example. Thecomposite article 20 is not limited to any particular type and may be,for example only, a turbine engine blade or vane, a leading edge of anairfoil, a support structure in a turbine engine, a combustor can orliner, a seal, joint or joining article, a rocket component, othercomponent over which hot exhaust gasses pass or other type of aerospacecomponent. Alternatively, the composite article 20 may be for any typeof application that would benefit from thermal and/or oxidativestability.

In the illustrated example, the composite article 20 includes asubstrate 22 and a ceramic nanocomposite layer 24 disposed on thesubstrate 22. Generally, the ceramic nanocomposite layer 24 protects theunderlying substrate 22 from a high temperature environment and/orcorrosive and oxidative environmental conditions. In this regard, theceramic nanocomposite layer 24 may be a coating on the substrate 22 or amatrix of a ceramic matrix composite, and the substrate 22 may be afiber in a ceramic matrix composite, the body of a component, a barrierlayer that is disposed on the body of a component, a matrix in which thenanocomposite layer 24 is disposed, or any other type of substrate thatwould benefit from the ceramic nanocomposite layer 24.

The substrate 22 may be a silicon-based ceramic material or a metallicmaterial. The silicon-based ceramic material may be silicon carbide(SiC), silicon nitride (Si₃N₄), silicon carbonitride, asilicon-carbon-nitrogen-containing ceramic material, or combinationsthereof, including oxygen-containing forms of these materials. In otherexamples, the substrate 22 may be a metallic material, such as asuperalloy. For instance, the superalloy may be a nickel-based orcobalt-based alloy. In any case, the substrate 22 would benefit fromadditional thermal and corrosion/oxidative resistance for the intendedend use. In this regard, the ceramic nanocomposite layer 24 facilitatesimproving the thermal and oxidative stability of the composite article20.

The ceramic nanocomposite layer 24 includes a composition havingsilicon, boron, carbon and nitrogen. In this disclosure, the term“nanocomposite” may refer to a multi-phase microstructure wherein one ormore of the phases includes at least one dimension that is less thanone-hundred nanometers. In some examples, the ceramic nanocompositelayer 24 may have more than one phase or all of its phases include atleast one dimension that is less than one-hundred nanometers. In afurther example, the ceramic nanocomposite layer 24 may have all of thedimensions of each phase be less than one-hundred nanometers. The term“nanocomposite” or “nanophase” in this disclosure is also used to referto materials that are considered amorphous, as determined by standardX-ray diffraction techniques, yet actually contain regions of ordered,crystalline phases with crystal grain dimensions or domains less thanone-hundred nanometers.

As will be described in more detail below, the particular nanophases ofthe ceramic nanocomposite layer 24 depend upon the processing methodsused to form a ceramic nanocomposite layer 24. In some examples, theceramic nanocomposite layer 24 may include silicon nitride (Si₃N₄) andboron nitride (BN). The boron nitride may be present in crystalline,amorphous or turbostratic forms. In other examples, the ceramicnanocomposite layer 24 may also include carbon in the composition. Thecarbon may be present within the microstructure in various forms, suchas silicon carbide (SiC), boron carbide (B₄C) or as regions of graphite,turbostratic carbon or graphene.

The composition of the ceramic nanocomposite layer 24 may be controlledduring processing by controlling a ratio, R, of silicon atoms to boronatoms. For instance, the ratio, R, of silicon atoms to boron atoms maybe 10≧R≧0.1. In a further example, the ratio, R, of silicon atoms toboron atoms may be 9≧R≧0.5, and in a further example the ratio may be3≧R≧1. The ratio, along with the selected processing parameters duringthe processing stage, control the composition and microstructure of thefinal ceramic nanocomposite layer 24. Thus, the ratio and processingparameters may be varied and controlled to yield particular compositionsand microstructures that are beneficial for the intended end useapplication.

FIG. 2 illustrates another embodiment composite article 120 that issomewhat similar to the composite article 20 shown in FIG. 1. In thisdisclosure, like reference numerals designate like elements whereappropriate, and reference numerals with the addition of one hundred ormultiples thereof designate modified elements that are understood toincorporate the same features and benefits of the corresponding originalelements. In this example, the composite article 120 includes a ceramicnanocomposite layer 124 disposed on the substrate 22. The ceramicnanocomposite layer 124 is identical to the ceramic nanocomposite layer24 but additionally includes an oxide-forming material 126 dispersedtherethrough.

The oxide-forming material 126 may include an oxide-forming metal orsemi-metal selected from aluminum, titanium, zirconium, hafnium,vanadium, niobium, tantalum, chromium, boron, molybdenum, tungsten,yttrium, ytterbium, scandium, rhenium, and combinations thereof. Theoxide-forming material 126 may be in elemental form or in compound form.In one example, the oxide-forming material 126 includes at leasthafnium. In other examples, the oxide-forming material 126 includes atleast zirconium and/or aluminum.

The oxide-forming material 126 serves as an oxygen scavenger by reactingwith available oxygen to form a stable oxide. The reaction with oxygenconsumes at least a portion of the available oxygen and thereby preventsthe oxygen from reacting with elements of the substrate 22 or elementsof any other adjacent materials. The example oxides are thermally stableand may physically expand to self-repair microcracks in the ceramicnanocomposite layer 124. The oxides may also react with elements of thesubstrate 22 or elements from any adjacent materials to form stablecompounds or glasses that further enhance the thermal stability of thecomposite article 120.

The oxide-forming material 126 may additionally or alternatively includea boride material. The boride material may include at least one borideof titanium, zirconium, hafnium, niobium, vanadium, tantalum andtungsten. The borides are thermally stable and may react with elementsof the substrate 22 or oxygen or elements from any adjacent materials toform stable compounds or glasses that further enhance the thermalstability of the composite article 120.

The oxide-forming material 126 may additionally or alternatively includea silicide material. The silicide material may include at least onesilicide of zirconium, hafnium, niobium, vanadium, titanium, tantalum,boron, molybdenum and tungsten. The silicides are thermally stable andmay react with elements of the substrate 22 or oxygen or elements fromany adjacent materials to form stable compounds or glasses that furtherenhance the thermal stability of the composite structure 120.

An example method of fabricating or processing the composite article 20or 120 may include forming the ceramic nanocomposite layer 24, 124 onthe substrate 22. That is, the substrate 22 may be pre-fabricated andthe ceramic nanocomposite layer 24, 124 may be formed on thepre-fabricated substrate 22. The particular technique selected forforming the ceramic nanocomposite layer 24, 124 may depend upon the typeof substrate 22, the desired end properties of the composite article 20,120 or a desire to use a certain process. In a few examples, chemicalvapor deposition with mixed volatile precursors, physical vapordeposition, thermal spray techniques, electrostatic or electrophoreticmethods or pre-ceramic polymer processing may be used. Given thisdescription, one of ordinary skill in the art will be able to recognizeadvantageous processing methods and parameters to meet their particularneeds.

In one example, the forming of the ceramic nanocomposite layer 24 mayinclude pre-ceramic polymer processing to achieve atomic level mixing ofthe constituent elements in appropriate ratios. For instance, theprocess may include pyrolyzing a single-source pre-ceramic polymer in acontrolled atmosphere such as nitrogen. The single-source pre-ceramicpolymer may be polyborosilazane with the desired ratio, R, of siliconatoms to boron atoms. That is, the single-source may be a singlepolymeric precursor structure rather than a mixture of two or morepre-ceramic precursor sources with the desired ratio, R, of siliconatoms to boron atoms.

The pyrolysis may be conducted in a known manner, and the pre-ceramicpolymer may be prepared in a known manner via reaction betweenorganosilicon compounds and boron compounds. In examples where theceramic nanocomposite layer 24, 124 includes the oxide-forming material126, the selected oxide-forming material or materials 126 along with anyother additives may be incorporated during the processing such that thefinal ceramic nanocomposite layer 24, 124 includes the oxide-formingmaterial or materials 126 and other additives. As an example, the metalor metals may be incorporated in metallic form by mixing with thepre-ceramic polymer prior to pyrolysis. Alternatively, the metal ormetals may be provided as organometallic compounds that are mixed withthe pre-ceramic polymer or precursors thereto. In another alternative,the metal or metals may be chemically incorporated into the polymerbackbone of the pre-ceramic polymer rather than being physically mixedwith the polymer. Likewise, the borides or silicides may be incorporatedin the pre-ceramic polymer prior to pyrolysis. The use of solvents toimprove dispersion of the oxide-forming material 126 is alsocontemplated. That is, the pre-ceramic polymer or the organometalliccompound may be dissolved in a suitable solvent and mixed to ensureuniform distribution of the components. Following removal of the solventthrough controlled heating and/or reduced pressure, a uniform mixturecontaining pre-ceramic polymer and oxide-forming material 126 isobtained.

The single source pre-ceramic polymer provides the benefit of an atomiclevel mixture of the elements of the composition of the ceramicnanocomposite layer 24, 124. Thus, the elements chemically bonded in thepre-ceramic polymer can remain following pyrolysis to form nanosizedphases or domains, rather than micro- or macro-sized phases thatcollectively have lower thermal/oxidative stability or otherdisadvantageous properties. Additionally, the single-source pre-ceramicpolymer can be pyrolyzed at temperatures below 1200° C. (2192° F.),which reduces thermal influence on the substrate 22. Higher temperaturesmay also be used to increase nanocrystal size or nanophase domain sizeor the extent of crystallinity of the phases, but may result inmicrostructures having less desirable phases or a substantial loss ofboron or other elements of the composition.

Additionally, as suggested above, the ratio of silicon atoms to boronatoms may be controlled during the preparation of the pre-ceramicpolymer to yield a final composition having a desired composition andproperties. That is, the ratio of silicon atoms to boron atoms in thepre-ceramic polymer corresponds to the ratio in the final ceramicnanocomposite layer 24, 124. Additionally, the silicon to boron ratioused in preparation of the pre-ceramic polymer, such aspolyborosilazane, may control the molecular weight of the pre-ceramicpolymer to tailor the polymer to certain processes. The pre-ceramicpolymer with the above exemplary ratios may be further characterized byits molecular weight range, which may be between 1000-500,000 atomicmass units or Daltons as measured by standard gel permeationchromatography methods.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

1. A composite article comprising: a substrate; and a ceramicnanocomposite layer disposed on the substrate, the ceramic nanocompositelayer having a composition comprising silicon, boron, carbon andnitrogen and at least one oxide-forming material selected from a groupconsisting of oxide-forming metals/semi-metals, borides, silicides, andcombinations thereof.
 2. The composite article as recited in claim 1,wherein the ceramic nanocomposite includes silicon nitride and boronnitride.
 3. The composite article as recited in claim 2, wherein thecarbon is in the form of silicon carbide, boron carbide, or combinationsthereof.
 4. The composite article as recited in claim 1, wherein thecomposition of the ceramic nanocomposite layer includes a ratio, R, ofsilicon atoms to boron atoms of 10≧R≧0.1.
 5. The composite article asrecited in claim 1, wherein the ratio, R, of silicon atoms to boronatoms is 3≧R≧1.
 6. The composite article as recited in claim 1, whereinthe oxide-forming metal is selected from a group consisting of aluminum,titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium,molybdenum, tungsten, yttrium, ytterbium, scandium, rhenium, andcombinations thereof.
 7. The composite article as recited in claim 6,wherein the oxide-forming metal includes hafnium.
 8. The compositearticle as recited in claim 6, wherein the oxide-forming metal includeszirconium.
 9. The composite article as recited in claim 6, wherein theoxide-forming metal includes aluminum.
 10. The composite article asrecited in claim 1, wherein the boride includes at least one metalselected from a group consisting of titanium, zirconium, hafnium,niobium, vanadium, titanium, tantalum, and tungsten.
 11. The compositearticle as recited in claim 1, wherein the silicide includes at leastone element selected from a group consisting of zirconium, hafnium,niobium, vanadium, titanium, tantalum, boron, molybdenum, and tungsten.12. The composite article as recited in claim 1, wherein the substrateis a silicon-based ceramic material or a metallic material.
 13. Acomposite article comprising: a silicon-based ceramic substrate; and aceramic nanocomposite layer disposed on the substrate, the ceramicnanocomposite layer having a composition comprising silicon, boron,carbon and nitrogen and at least one oxide-forming material selectedfrom a group consisting of aluminum, titanium, zirconium, hafnium,vanadium, niobium, tantalum, chromium, molybdenum, tungsten, yttrium,ytterbium, scandium, rhenium, and combinations thereof.
 14. Thecomposite article as recited in claim 13, wherein the oxide-formingmaterial includes hafnium.
 15. The composite article as recited in claim13, wherein the oxide-forming material includes zirconium.
 16. Thecomposite article as recited in claim 13, wherein the oxide-formingmaterial includes aluminum.
 17. The composite article as recited inclaim 13, wherein the composition of the ceramic nanocomposite layerincludes a ratio, R, of silicon atoms to boron atoms of 10≧R≧0.1.
 18. Amethod of processing a composite article, comprising: forming a ceramicnanocomposite layer having a composition that includes silicon, boron,carbon and nitrogen on a substrate.
 19. The method as recited in claim18, wherein the forming of the ceramic nanocomposite layer includespyrolyzing a single-source pre-ceramic polymer.
 20. The method asrecited in claim 18, wherein the forming of the ceramic nanocompositelayer includes pyrolyzing a polyborosilazane pre-ceramic polymer. 21.The method as recited in claim 18, wherein the forming of the ceramicnanocomposite layer is conducted at a temperature below about 1200° C.22. The method as recited in claim 18, wherein the forming of theceramic nanocomposite includes using a pre-ceramic polymer having amolecular weight of 1000-500,000 atomic mass units.